FIG. 1 illustrates a network including a plurality of cells. Specifically, FIG. 1(a) is a view illustrating a heterogeneous network wireless communications system including a macro Base Station (BS), BS A, and a micro BS, BS B, and FIG. 1(b) is a view illustrating a homogeneous network wireless communications system including macro BSs, BS A and BS B.
The heterogeneous network refers to a network where a macro BS and a micro BS co-exist even when the same Radio Access Technology (RAT) is used. The homogeneous network refers to a network comprised of macro BSs or a network comprised of micro BSs.
A macro BS represents a normal BS of a wireless communication system, having broad coverage (service area) and high transmission power. A geographic area in which a communication service is provided by a macro BS and BS A may be referred to as a macro cell. For example, a pico BS, a femto BS, or a relay may be the micro BS. A geographic area in which a communication service is provided by the micro BS, BS B, may be referred to as a micro cell, a pico cell, or a femto cell. The micro BS corresponds to a small-scale version of the macro BS. Accordingly, the micro BS may independently operate while performing most of the functions of the macro BS. The micro BS may be installed in an area covered by the macro BS (overlay type) or may be installed in a shadow area that cannot be covered by the macro BS (non-overlay type). As compared to the macro BS, the micro BS has a narrower coverage range and lower transmission power and may accommodate a smaller number of User Equipments (UEs).
Referring to FIG. 1(a), UEs, UE0 and UE1, may directly served by the macro BS A (hereinafter, such UEs are referred to as macro-UEs). A UE, UE2, may directly receive services from the micro BS (hereinafter such a UE is referred to as a micro-UE). In some cases, UE2 in the coverage area of the micro BS may receive services from the macro BS. In FIG. 1(a), it is assumed that UE2 is connected to the micro BS B.
Depending upon whether or not UE access is restricted, the micro BS may be categorized into two different types, the first type being a Closed Subscriber Group (CSG) micro BS and the second type being an Open Access (OA) or Open Subscriber Group (OSG) micro BS. The CSG micro BS may serve only specific UEs that are authorized and the OSG micro BS may serve all UEs without any particular access limitations.
As illustrated in FIG. 1(a), when UE2 served by the micro BS in a heterogeneous network receives a desired signal from the micro BS, UE2 may be subjected to interference by a strong signal transmitted from the macro BS. As another example, if UE1 served by the macro BS is adjacent to the micro BS as shown in FIG. 1(a), interference may be generated in a signal that UE1 receives from the macro BS by a strong signal from the micro BS. Such interference is referred to as inter-cell interference. While inter-cell interference generated on downlink (DL) from the BS to the UE has been described in the above examples, inter-cell interference may occur even on uplink (UL) from the UE to the BS.
Inter-cell interference may be generated in not only the heterogeneous network as shown in FIG. 1(a) but also the homogeneous network as shown in FIG. 1(b). Referring to FIG. 1(b), when UE2 which is served by the macro BS B and located at an edge of the cells A and B, which are served by the macro BSs, BS A and BS B, respectively receives a desired signal from the macro BS B, UE2 may be subjected to interference by a signal from the macro BS A. Alternatively, when UE1, which is located at a cell edge while being served by the macro BS A, receives a signal from the macro BS A, UE1 may be subjected to interference by a signal from the macro BS B adjacent to the macro BS A as shown in FIG. 1(b). A UL signal from the UE to the BS, as well as a DL signal from the BS to the UE, may also function as interference with respect to a neighboring cell.
Such mutual interference between cells causes deterioration of cell throughput. Furthermore, in the event of severe interference, network failure may occur.